Think of your Droid like a mini PC. When CPU and/or GPU utilization are high, the device is going to start kicking out heat. There's a high performance chipset in this little package, and it doesn't even have the luxury of a fan to keep it cool. The casing of the phone basically acts like one large heatsink. And when battery demand is high, the battery will produce additional heat. I'd say too hot would be when it actually becomes uncomfortable to hold.

Other than that, spontaneous reboots and/or random lockups can be symptoms of an overheating condition; either the CPU or memory. Graphical corruption (artifacting) can also be a sign that the graphics core is overheating. Basically the same symptoms of an overheating PC.

There have been other discussions about heat, but I was never able to find out if "noticeably warm" is normal. While at rest (and stand-by), the phone feels cool. When charging and playing intense games, the back of the phone feels warm to the touch. Not hot, and not uncomfortable, but noticeably warm. I expect it under those conditions; as has been stated, it's really a portable computer.

But this morning, there were 9 applications that were updated in the market. So I downloaded and installed all of the updates. During the process, the back of the phone (near the camera lens) got noticeably warmer (which happens whenever I use the Internet more than briefly); again, not what I would define as "hot", but a little warmer than "casually warm" (I also understand that my hand will also warm the area when I'm holding the phone). Using the battery widget, I've never seen the temperature go over 100 degrees F.

All of this to simply ask "is this normal; does everyone experience this behavior?" I can certainly live with it, but if there's something wrong with the device, I'd rather exchange it now than wait for something to go catastrophically wrong because of the heat. Can anyone offer me peace of mind?